Effects of ventilation on the surfactant system in sepsis-induced lung injury

Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

The impact of maternal protein restriction during perinatal life on the response to a septic insult in adult rats

Although abundant evidence exists that adverse events during pregnancy lead to chronic conditions, there is limited information on the impact of acute insults such as sepsis. This study tested the hypothesis that impaired fetal development leads to altered organ responses to a septic insult in both male and female adult offspring. Fetal growth restricted (FGR) rats were generated using a maternal protein-restricted diet. Male and female FGR and control diet rats were housed until 150-160 d of age when they were exposed either a saline (control) or a fecal slurry intraperitoneal (Sepsis) injection. After 6 h, livers and lungs were analyzed for inflammation and, additionally, the amounts and function of pulmonary surfactant were measured. The results showed increases in the steady-state mRNA levels of inflammatory cytokines in the liver in response to the septic insult in both males and females; these responses were not different between FGR and control diet groups. In the lungs, cytokines were not detectable in any of the experimental groups. A significant decrease in the relative amount of surfactant was observed in male FGR offspring, but this was not observed in control males or in female animals. Overall, it is concluded that FGR induced by maternal protein restriction does not impact liver and lung inflammatory response to sepsis in either male or female adult rats. An altered septic response in male FGR offspring with respect to surfactant may imply a contribution to lung dysfunction.

Impact of mechanical ventilation on the pathophysiology of progressive acute lung injury

The earliest description of what is now known as the acute respiratory distress syndrome (ARDS) was a highly lethal double pneumonia. Ashbaugh and colleagues (Ashbaugh DG, Bigelow DB, Petty TL, Levine BE Lancet 2: 319-323, 1967) correctly identified the disease as ARDS in 1967. Their initial study showing the positive effect of mechanical ventilation with positive end-expiratory pressure (PEEP) on ARDS mortality was dampened when it was discovered that improperly used mechanical ventilation can cause a secondary ventilator-induced lung injury (VILI), thereby greatly exacerbating ARDS mortality. This Synthesis Report will review the pathophysiology of ARDS and VILI from a mechanical stress-strain perspective. Although inflammation is also an important component of VILI pathology, it is secondary to the mechanical damage caused by excessive strain. The mechanical breath will be deconstructed to show that multiple parameters that comprise the breath-airway pressure, flows, volumes, and the duration during which they are applied to each breath-are critical to lung injury and protection. Specifically, the mechanisms by which a properly set mechanical breath can reduce the development of excessive fluid flux and pulmonary edema, which are a hallmark of ARDS pathology, are reviewed. Using our knowledge of how multiple parameters in the mechanical breath affect lung physiology, the optimal combination of pressures, volumes, flows, and durations that should offer maximum lung protection are postulated.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Evolution of surfactant protein-D levels in children with ventilator-associated pneumonia

RATIONALE

The pathobiology of ventilator-associated pneumonia (VAP) in children is poorly understood; investigation has been limited by lack of universally applied diagnostic criteria and reliable biomarkers for this condition.

OBJECTIVES

We evaluated the clinical pulmonary infection score (CPIS) in diagnosing VAP and prospectively characterized the relationship between surfactant protein-D (SP-D) metabolism and VAP.

METHODS

Children admitted to an Egyptian PICU requiring intubation were screened for the absence of primary pulmonary pathology. Thirty-nine children underwent two evaluations: during the first 36 hr following intubation and after 4 days of mechanical ventilation. During both, bronchoalveolar lavage fluid (BALF) was obtained for culture and SP-D assay. CPIS was computed during the second evaluation.

RESULTS

Optimum performance of the CPIS against BALF culture occurred at a cutoff value of 6, (ROC AUC of 0.89 ± 0.05). Children who developed VAP had significantly higher SP-D levels, both preceding (129.9 ± 33.5 ng/ml at the 1st BAL)-and following positive BALF culture (249.5 ± 51.2 ng/ml at the 2nd BAL), compared to children whose BALF remained sterile (62.6 ± 18.1 ng/ml and 64.9 ± 9.4 ng/ml; P < 0.001). This increase in SP-D levels was most evident in children infected with Pseudomonas aeruginosa compared to children with Klebsiella pneumonia or S. aureus.

CONCLUSIONS

The CPIS performed well against BALF culture. We observed a bacterial species-specific difference in SP-D levels in children who developed VAP; this change preceded detection of infection by CPIS or BALF culture.

Computed tomography assessment of exogenous surfactant-induced lung reaeration in patients with acute lung injury

Introduction

Previous randomized trials failed to demonstrate a decrease in mortality of patients with acute lung injury treated by exogenous surfactant. The aim of this prospective randomized study was to evaluate the effects of exogenous porcine-derived surfactant on pulmonary reaeration and lung tissue in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS).

Methods

Twenty patients with ALI/ARDS were studied (10 treated by surfactant and 10 controls) in whom a spiral thoracic computed tomography scan was acquired before (baseline), 39 hours and 7 days after the first surfactant administration. In the surfactant group, 3 doses of porcine-derived lung surfactant (200 mg/kg/dose) were instilled in both lungs at 0, 12 and 36 hours. Each instillation was followed by recruitment maneuvers. Gas and tissue volumes were measured separately in poorly/nonaerated and normally aerated lung areas before and seven days after the first surfactant administration. Surfactant-induced lung reaeration was defined as an increase in gas volume in poorly/non-aerated lung areas between day seven and baseline compared to the control group.

Results

At day seven, surfactant induced a significant increase in volume of gas in poorly/non-aerated lung areas (320 ± 125 ml versus 135 ± 161 ml in controls, P = 0.01) and a significant increase in volume of tissue in normally aerated lung areas (189 ± 179 ml versus -15 ± 105 ml in controls, P < 0.01). PaO₂/FiO₂ ratio was not different between the surfactant treated group and control group after surfactant replacement.

Conclusions

Intratracheal surfactant replacement induces a significant and prolonged lung reaeration. It also induces a significant increase in lung tissue in normally aerated lung areas, whose mechanisms remain to be elucidated.

Trial registration

NCT00742482.

[Value of surfactant replacement therapy in the treatment of acute respiratory distress syndrome]

Acute respiratory distress syndrome (ARDS) is a common, devastating clinical problem arising from a number of conditions, such as pneumonia, trauma or sepsis. Because of its significant mortality and morbidity, ARDS has been in the focus of extensive experimental and clinical research. Since there is little doubt that alterations of the surfactant system contribute to lung dysfunction and the onset of ARDS, several clinical studies examined the therapeutic safety and efficacy of a surfactant replacement therapy. Clinical experience with exogenous surfactant has proven inconsistent as a therapeutic modality for adult patients with ARDS. This is mainly due to a number of confounding factors, e.g. severity of injury at the time of treatment, dosing regimes and delivery methods used in different trials. However, current data suggest that patients with direct ARDS (e.g. pneumonia, aspiration) could benefit from surfactant replacement therapy rather than patients with indirect ARDS (e.g. sepsis, trauma). Although surfactant replacement therapy has been shown to significantly reduce mortality in neonates with ARDS, there has been no large randomised clinical trial showing that exogenous surfactant improves outcome in adults with respiratory failure. Therefore, surfactant therapy cannot be recommended for routine clinical use in adult patients and has to be considered as a last resort treatment.

Positive pressure ventilation: what is the real cost?

Positive pressure ventilation is a radical departure from the physiology of breathing spontaneously. The immediate physiological consequences of positive pressure ventilation such as haemodynamic changes are recognized, studied, and understood. There are other significant physiological interactions which are less obvious, more insidious, and may only produce complications if ventilation is prolonged. The interaction of positive pressure with airway resistance and alveolar compliance affects distribution of gas flow within the lung. The result is a wide range of ventilation efficacy throughout different areas of the lung, but the pressure differentials between alveolus and interstitium also influence capillary perfusion. The hydrostatic forces across the capillaries associated with the effects of raised venous pressures compound these changes resulting in interstitial fluid sequestration. This is increased by impaired lymphatic drainage which is secondary to raised intrathoracic pressure but also influenced by raised central venous pressure. Ventilation and PEEP promulgate further physiological derangement. In theory, avoiding these physiological disturbances in a rested lung may be better for the lung and other organs. An alternative to positive pressure ventilation might be to investigate oxygen supplementation of a physiologically neutral and rested lung. Abandoning heroic ventilation would be a massive departure from current practice but might be a more rationale approach to future practice.

Protective effects of elevated endogenous surfactant pools to injurious mechanical ventilation

Depletion of alveolar macrophages (AM) leads to an increase in endogenous surfactant that lasts several days beyond the repletion of AM. Furthermore, impairment to the endogenous pulmonary surfactant system contributes to ventilation-induced lung injury. The objective of the current study was to determine whether increased endogenous surfactant pools induced via AM depletion was protective against ventilation-induced lung injury. Adult rats were intratracheally instilled with either control or dichloromethylene diphosphonic acid (DMDP) containing liposomes to deplete AMs and thereby increase endogenous surfactant pools. Either 3 or 7 days following instillation, rats were exposed to 2 h of injurious ventilation using either an ex vivo or in vivo ventilation protocol and were compared with nonventilated controls. The measured outcomes were oxygenation, lung compliance, lavage protein, and inflammatory cytokine concentrations. Compared with controls, the DMDP-treated animals had significantly reduced AM numbers and increased surfactant pools 3 days after instillation. Seven days after instillation, AM numbers had returned to normal, but surfactant pools were still elevated. DMDP-treated animals at both time points exhibited protection against ventilation-induced lung injury, which included superior physiological parameters, lower protein leakage, and lower inflammatory mediator release into the air space, compared with animals not receiving DMDP. It is concluded that DMDP-liposome administration protects against ventilation-induced lung injury. This effect appears to be due to the presence of elevated endogenous surfactant pools.

Adjunctive therapy to mechanical ventilation: surfactant therapy, liquid ventilation, and prone position

Acute lung injury and acute respiratory distress syndrome are associated with significant morbidity and mortality in critically ill patients. Although lung protective mechanical ventilation is the only therapy shown to reduce mortality and development of organ failure, several biologic pathways have been identified and provided an opportunity for therapeutic interventions. No pharmacologic or adjunctive treatments are available. Clinical studies demonstrated that prone position results in significant and clinically relevant improvement in oxygenation and ventilation, which persist when patients are returned to supine position; the beneficial response is not limited to patients turned early in disease course. Few complications are associated with prone ventilation. Clinical experience suggests that prone ventilation may protect the lung from potential detrimental effects of mechanical ventilation. Further studies are needed.

Volutrauma activates the clotting cascade in the newborn but not adult rat

Coagulopathy and alveolar fibrin deposition are common in sick neonates and attributed to the primary disease, as opposed to their ventilatory support. Hypothesizing that high tidal volume ventilation activates the extrinsic coagulation pathway, we air ventilated newborn and adult rats at low (10 ml/kg) or high (30 ml/kg) tidal volume and compared them with age-matched nonventilated controls. Blood was collected at the end of the experiment for measurement of clot time, tissue factor, and other coagulation factor content. Similar measurements were obtained from lung lavage material. The newborn clot time (44+/-1) was lower and plasma tissue factor content higher (103.4+/-0.4) than adults (88+/-4 s and 26.6+/-1.4 units; P<0.01). High, but not low, tidal volume ventilation of newborns for as little as 15 min significantly reduced clot time and increased plasma tissue factor content (P<0.01). High volume ventilation increased plasma factor Xa (0.1+/-0.1 to 1.6+/-0.4 nM; P<0.01) and thrombin (1.3+/-0.2 to 2.2+/-0.4 nM; P<0.05) and decreased antithrombin (0.12+/-0.01 to 0.05+/-0.01; P<0.01) in the newborn. Lung lavage material of high volume-ventilated newborns showed increased (P<0.01) factor Xa and thrombin. No changes in these parameters were observed in adult rats that were high volume ventilated for up to 90 min. Compared with adults, newborn rats have a greater propensity for volutrauma-activated intravascular coagulation. These data suggest that mechanical ventilation promotes neonatal thrombosis via lung tissue factor release.

Cellular stress failure in ventilator-injured lungs

The clinical and experimental literature has unequivocally established that mechanical ventilation with large tidal volumes is injurious to the lung. However, uncertainty about the micromechanics of injured lungs and the numerous degrees of freedom in ventilator settings leave many unanswered questions about the biophysical determinants of lung injury. In this review we focus on experimental evidence for lung cells as injury targets and the relevance of these studies for human ventilator-associated lung injury. In vitro, the stress-induced mechanical interactions between matrix and adherent cells are important for cellular remodeling as a means for preventing compromise of cell structure and ultimately cell injury or death. In vivo, these same principles apply. Large tidal volume mechanical ventilation results in physical breaks in alveolar epithelial and endothelial plasma membrane integrity and subsequent triggering of proinflammatory signaling cascades resulting in the cytokine milieu and pathologic and physiologic findings of ventilator-associated lung injury. Importantly, though, alveolar cells possess cellular repair and remodeling mechanisms that in addition to protecting the stressed cell provide potential molecular targets for the prevention and treatment of ventilator-associated lung injury in the future.

Mechanical ventilation effect on surfactant content, function, and lung compliance in the newborn rat

Studies of ventilator-associated lung injury in adult experimental animal models have documented that high tidal volume (TV) results in lung injury characterized by impaired compliance and dysfunctional surfactant. Yet, there is evidence that, in neonates, ventilation with a higher than physiologic TV leads to improved lung compliance. The purpose of our study was to evaluate how lung compliance and surfactant was altered by high TV ventilation in the neonate. We utilized a new model (mechanically air-ventilated newborn rats, 4-8 d old), and used 40 or 10 mL/kg TV strategies. Age-matched nonventilated animals served as controls. In all animals, dynamic compliance progressively increased after initiation of mechanical ventilation and was significantly greater than basal values after 60 min (p < 0.01). Lung lavage total surfactant with both TV strategies (p < 0.05) and the large aggregate fraction (only in TV = 40 mL/kg; p < 0.01) were significantly increased by 60 min of mechanical ventilation, compared with control animals. Ventilation with 40 mL/kg TV for 60 min adversely affected the lung surfactant surface-tension lowering properties (p < 0.01). After 180 min of ventilation with 40 mL/kg TV, the lung total surfactant content and dynamic compliance values were no longer distinct from the nonventilated animals' values. We conclude that, in the newborn rat, mechanical ventilation with a higher than physiologic TV increases alveolar surfactant content and, over time, alters its biophysical properties, thus promoting an initial but transient improvement in lung compliance.

Hyperoxia exposure impairs surfactant function and metabolism

OBJECTIVE

To evaluate the effects of hyperoxia exposure on lung function and the endogenous surfactant system in spontaneously breathing adult rats.

DESIGN

Analysis of the pulmonary surfactant system isolated from adult rats following exposure to > 90% oxygen or room air for 48 or 72 hrs.

SETTING

A basic science research laboratory in a university setting.

SUBJECTS

Sixty pathogen-free Sprague-Dawley rats.

INTERVENTIONS

Exposure to > 90% oxygen for 72 hrs.

MEASUREMENTS AND MAIN RESULTS

Exposure to > 90% oxygen for 72 hrs resulted in significant lung dysfunction and an increase in neutrophils and total protein concentrations within the airspace compared with animals exposed to room air or 48 hrs of 90% oxygen exposure. Total alveolar surfactant and large aggregate pool sizes were increased after 72 hrs of hyperoxia compared with the other groups, and there was evidence of lipid peroxidation within these large aggregate subtractions. The biophysical function of large aggregate isolated from 72-hr hyperoxia-exposed animals was also impaired and converted into small aggregate forms faster than large aggregate from normoxia-exposed animals when assessed using in vitro surface area cycling techniques.

CONCLUSIONS

Oxidative stress on the endogenous surfactant system may represent an important mechanism contributing to the surfactant dysfunction and abnormal surfactant metabolism associated with hyperoxia-induced lung injury.

Methylprednisolone effects on oxygenation and histology in a rat model of acute lung injury

We examined the effects of methylprednisolone on gas exchange, pressure-volume curve, lavage fluid inflammatory cell counts, protein content, surfactant pool size, and lung histology in a rat model of paraquat-induced lung injury. Twenty-three adult male Sprague-Dawley rats received intraperitoneal paraquat injection (35 mg/kg) and were randomly divided into three groups: (1). control group received no further treatment; (2). 1-dose methylprednisolone group received a concomitant intraperitoneal methylprednisolone injection (30 mg/kg); (3). 3-dose methylprednisolone group received a concomitant and daily intraperitoneal methylprednisolone injection (30 mg/kg) for three doses. Three days after paraquat injection, the rat was ventilated for 90 min, a static pressure-volume curve and bronchoalveolar lavage was performed, and postmortem histology was examined. Surfactant pool size of the 3-dose methylprednisolone group was significantly increased when compared with the control and 1-dose methylprednisolone groups. Methylprednisolone treatment increased oxygenation and the value was statistically significant for 3-dose methylprednisolone group at 90 min of ventilation. Inflammatory cell counts in bronchoalveolar lavage fluid and lung injury score were decreased as the methylprednisolone dose increased. We conclude that high-dose methylprednisolone treatment increased surfactant pool size and improved lung histology of paraquat-injured lungs but this augmentation could not significantly improve oxygenation throughout the ventilation period.

The role of exogenous surfactant in the treatment of acute lung injury

A number of conditions, such as pneumonia, trauma, or systemic sepsis arising from the gut, may result in the acute respiratory distress syndrome (ARDS). Because of its significant morbidity and mortality, ARDS has been the focus of extensive research. One specific area of interest has been the investigation of the role of the surfactant system in the pathophysiology of this disease. Several studies have demonstrated that alterations of surfactant contribute to the lung dysfunction associated with ARDS, which has led to investigations into the use of exogenous surfactant as a therapy for this syndrome. Clinical experience with surfactant therapy has been variable owing to a number of factors including the nature of the injury at the time of treatment, the specific surfactant preparation utilized, the dose and delivery method chosen, the timing of surfactant administration over the course of the disease, and the mode of ventilation used during and after surfactant administration.

Early surfactant administration protects against lung dysfunction in a mouse model of ARDS

Sepsis can predispose the lung to insults such as mechanical ventilation (MV). It was hypothesized that treating the lung with exogenous surfactant early in the development of sepsis will reduce the lung dysfunction associated with MV 18 h later. Mice underwent sham or cecal ligation and perforation (CLP) surgery. Immediately after surgery, mice were either untreated or given 100 mg/kg of bovine lipid extract surfactant intratracheally. Eighteen hours later, the lungs were removed and analyzed either immediately or following ventilation ex vivo for 2 h by an "injurious" mode of ventilation (20 ml/kg, 0 cm positive end-expiratory pressure). In nonventilated lungs, exogenous surfactant had no impact on compliance or IL-6 concentrations in the lungs. In the ventilated groups, the administered surfactant had a significant protective effect on the lung dysfunction induced by MV, but only in the CLP lungs. We conclude that administration of exogenous surfactant at the time of a systemic insult can protect the lung from the damaging effects of MV 18 h later.

Response of alveolar cells to mechanical stress

The purpose of this review is to highlight areas in alveolar cell biology in which our understanding of the effects of mechanical stress have been advanced in the last year, focusing on intracellular signal transduction pathways, the surfactant system, and cell injury and repair. Mechano-transduction pathways are only now beginning to be elucidated in alveolar cells. The importance of the mitogen-activated protein kinase, G protein, and growth factor systems is emphasized. The research conducted in the last year has also stressed the importance of alveolar cell cross-talk, with surfactant exocytosis being facilitated through parathyroid hormone-related peptide and leptin and calcium in interstitial fibroblasts and endothelial cells, respectively. Finally, the importance of deformation-induced plasma membrane breaks is emphasized. Alveolar cells were found to exocytose intracellular lipid vesicles to the plasma membrane-not only to prevent cell breaks but also to reseal cell breaks. This dynamic process was a stronger determinant of cell breaks than the prestress properties of the cytoskeleton. All of these exciting findings provide further potential treatment targets for ventilator-induced lung injury.

Conventional mechanical ventilation of healthy lungs induced pro-inflammatory cytokine gene transcription

We investigated the potential inflammatory reaction induced by mechanical ventilation (MV) using 10 ml/kg tidal volume and no positive end-expiratory pressure (PEEP) in control (C, n = 8), spontaneously breathing (SB, n = 12) and mechanically ventilated (MV, n = 12) rabbits with normal lungs. After 6 h (MV and SB groups) or immediately (C group), lungs were removed for measurement of wet-to-dry (W/D) weight ratio and for bronchoalveolar lavage (BAL). Pulmonary mechanics were also studied. MV animals developed a modest but significant (P < 0.01) impairment of arterial blood oxygenation and had higher W/D lung weight ratio than C ones. In MV group, BAL macrophage count was greater (P < 0.05) than in SB one. MV induced an upregulation of MCP-1, TNF-alpha, and IL-1beta gene transcription (mRNAs), without significant elevation of the corresponding protein cytokines in the BAL supernatant, except for MCP-1 (P < 0.05). These data suggest that MV, even using moderate tidal volume, elicits a pro-inflammatory stimulus to the lungs.

Mechanical ventilation of isolated rat lungs changes the structure and biophysical properties of surfactant

Mechanical ventilation is an essential but potentially harmful therapeutic intervention for patients with acute lung injury. The objective of this study was to investigate the effects of mechanical ventilation on large-aggregate surfactant (LA) structure and function. Isolated rat lungs were randomized to either a nonventilated control group, a relatively noninjuriously ventilated group [1 h, 10 ml/kg tidal volume, 3 cmH(2)O positive end-expiratory pressure (PEEP)], or an injuriously ventilated group (1 h, 20 ml/kg tidal volume, 0 cmH(2)O PEEP). Injurious ventilation resulted in significantly decreased lung compliance compared with the other two groups. LA structure, as determined by electron microscopy, revealed that LA from the injurious group had significantly lower amounts of organized lipid-protein structures compared with LA obtained from the other groups. Analysis of the biophysical properties by using a captive bubble surfactometer demonstrated that adsorption and surface tension reduction were significantly impaired with LA from the injuriously ventilated lungs. We conclude that the injurious mechanical ventilation impairs LA function and that this impairment is associated with significant morphological alterations.

Polyethylene glycol (PEG) attenuates exogenous surfactant in lung-injured adult rabbits

Exogenous surfactant administration in patients with the acute respiratory distress syndrome is currently being evaluated, although resource limitations and the potential expense are existing concerns. Previous in vitro and in vivo studies have shown that substances such as polyethylene glycol (PEG) added to exogenous surfactant improved the function of the surfactant. Based on these data, we hypothesized that PEG would augment surfactant function in an adult rabbit model of lung injury induced by lung lavage and mechanical ventilation, and that this would be accomplished by altering surfactant metabolism. Contrary to our hypothesis, however, mean Pa(O(2)), Pa(CO(2)), and peak inspiratory pressures values 3 h after treatment were significantly worse in the surfactant + PEG treatment groups compared with the surfactant alone groups. These effects were observed for two different doses of surfactant tested. Lavage analyses after sacrifice showed that animals given PEG with their surfactant had significantly lower total and large aggregate surfactant pool sizes compared with animals given surfactant alone. We conclude that in this lung injury model, PEG attenuated surfactant responses, suggesting that further preclinical studies are required before testing this approach in humans.

Pulmonary surfactant and inflammation in septic adult mice: role of surfactant protein A

Surfactant alterations, alveolar cytokine changes, and the role of surfactant protein (SP)-A in septic mice were investigated. Sepsis was induced via cecal ligation and perforation (CLP). Septic and sham mice were euthanized at 0, 3, 6, 9, 12, 15, and 18 h after surgery. Mice deficient in SP-A and mice that overexpressed SP-A were euthanized 18 h after surgery. In wild-type, sham-operated mice, surfactant pool sizes were similar at all time points, whereas in the CLP groups there was a significant decrease in small-aggregate surfactant pool sizes beginning 6 h after CLP. Interleukin-6 concentrations in bronchoalveolar lavage fluid from septic animals increased from 6 to 18 h after surgery. Identical surfactant alterations and concentrations of cytokines were observed in septic mice that were SP-A deficient or that overexpressed SP-A. In conclusion, alterations of pulmonary surfactant and alveolar cytokines occur simultaneously, 6 h after a systemic insult. In addition, we did not detect a role for SP-A in regulating surfactant phospholipid pool sizes or pulmonary inflammation in septic mice.